Study of cavitation and failure mechanisms of a superplastic 5083 aluminum alloy

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Superplastic forming of AA5083 is an economical way to create components of complex shape while retaining the high strength and stiffness-to-weight ratios associated with aluminum alloys. However, failure of the material due to formation and linkage of cavities during superplastic deformation poses a major obstacle in effective industrial employment of this technology. Deformed samples of AA5083 were analyzed by various techniques after superplastic deformation under uniaxial tension, biaxial tension, or plane strain conditions. The goal was to determine the roles of MnAl6 second phase particles and the grain boundary disorientations in the processes of cavity formation and growth. Scanning electron microscopy (SEM) techniques included backscatter imaging (BSI), energy dispersive spectrometry (EDS) and orientation imaging microscopy (OIM) to identify and evaluate sites of cavity formation in these samples. Results of this study show that cavities form due to grain boundary sliding (GBS) and separation of boundaries. Second phase particles such as MnAl6 were apparent on some separating boundaries but not on others. Cavities also grow from pre-existing voids introduced during prior processing. The role of GBS was confirmed by evaluating the grain-to-grain disorientations across newly formed small cavities. Results show that these disorientations are [greater than] 7 [degrees], a value consistent with the threshold value of disorientation for GBS in pure Aluminum.

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